You have a black/blue which is not neutral but return from switch and you have tried to use it as a neutral. The normal ceiling rose has three cables feed in, feed to next lamp, switch. The latter is often a standard brown and blue or old colours red and black cable and a brown or red sleeve is put on the blue or black wire to show it can be live not neutral. I think this wire is mixed up with neutrals. See other posts or maybe now on projects on how two work it out if you have lost sleeve. Since you are not using standard rose yours will be a little different.
Made progress last night..... after snapping my mains tester screwdriver that is!
I got the hall /outside lights working together with one of the new lounge lights.
Basically I took it all apart and connected the two reds in lamp 1, earths together, blue & blaclk together which left a yellow wire.
On lamp 2 3 reds went together, one which was the input from the other lamp on the circuit, one which went to the switch and the other to the hall continuing the circuit. The 4th red was the return from the switch. In addition, I connected the blue & Black together and the earths. The connections are all with 5a strip connectors.
Having tested the connections with a neighbour's tester plus a pendant lamp first, I proceeded to fit the new lamp which worked fine.
I connected the pendant to lamp 1 with a coonection to the black/blue and to the yellow but this didn't work. The hall & lamp 2 work fine.
I can only presume that shoving the terminals throough the ceiling has disturbed the connection to lamp 1 maybe?
Glad to here you got most of it working. The fact you have three core and earth at the light makes it non standard and very hard to advise. Properly you are correct in looking for disturbed wire. But being non standard maybe its time to accept your limitations and get an electrician?
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